Expandable cavity-backed spiral antenna



Feb. 10, 19'50 R. A. FARRAN T EXPANDABLE CAVITY-BACKED SPIRAL ANTENNAFiled Feb. 12. 1968 'fFIE. 1

on T 5 mm H W M Na N A Wm m mw 5 r 2 p 2 H Z United States Patent O US.Cl. 343-834 6 Claims ABSTRACT OF THE DISCLOSURE An expandable fiat,cavity-backed spiral antenna designed to be light in weight, stored in asmall volume and expanded to close tolerances with great reliabilityincluding a plurality of spring loaded folding arms mounted about acentral shaft and flexible antenna surfaces attached to the center postand arms which fold completely and extend in near perfect parallel planeduring operation.

BACKGROUND OF THE INVENTION This invention relates generally toexpandable antennas and more specifically to a method and means forcompactly storing and reliably displaying a close tolerance, flat,cavity-backed expandable spiral antenna.

A flat, cavity-backed spiral antenna is often desirable whencommunication is required over a Wide range of frequencies. This type ofantenna consists generally of two flat, parallel surfaces; one surfaceis used as a structural support for one or more pairs of individualspirals, the other surface serves as a reflector to amplify the signalsemitted and received by the spirals. The spirals emanate from the centerof the surface, a coaxial cable is used to feed each spiral at thiscentral point. This surface which supports the spirals is transparent toRF radiation.

In space applications, it is necessary during propulsion of a spacevehicle into orbit to provide a regular shaped object in order tominimize drag and avoid complications in guiding the lifting vehicle.Once in orbit, outer coverings fall away on command and the essentialparts are left exposed to perform their assigned tasks. The problem thatarises, however, is to store large devices within this relatively smallregular shaped nose cone. The storage volume constraint Within thespacecraft has necessitated the use of expandable antennas havingexpandable diameters of five to ten feet. In the case of deep spaceprobes, antennas of even larger diameters may be needed.

In the past, antennas of various configurations and mechanical andchemical combinations have been proposed but fail to meet the rigidrequirements of volume, weight, and reliability. Examples of prior artdevices include an expandable flexible disk wherein a spiral surface isattached to a rigid thin-shell structure. The disadvantage of such adevice is that for large antenna diameters the packaging within arestricted spacecraft volume is diflicult, if not imposible. Anothermechanical antenna consists of a box-shape support frame which expandsinto an antenna configuration. This antenna likewise fails to meet thespace requirement because of the many mechanical components needed toform this shape. Still another type of antenna is the internal orexternal flex rib antenna. The device utilizes the spring action of ribswound around a center hub to display the antenna. When a band or similardevice which restrains the ribs is released, the ribs are free to springinto their extended position. This antenna fails to meet the closetolerances needed to insure reliability.

3,495,250 Patented Feb. 10, 1970 A further example of the prior artconsists of an elastic recovery foam antenna wherein an elastic recoveryform or sponge-like material is used to display the antenna surfaces.The foam has a spoked-wheel shape over which the antenna surfaces arestretched. The antenna is compressed into a number of folds duringpackaging and, upon release, the foam assumes its original shape,thereby deploying the antenna. In this design, the antenna surfaces arefully supported by the foam. This antenna is particularly susceptible tofailure in that foam or other sponge-like material fails to assume thecontour to the accuracy required for this application. Similarly, sincefoam tends to lose some of its resiliency under prolonged compression,it has very limited shelf life and should be used almost immediatelyafter manufacturing.

Other types of prior art antennas which have been proposed for use inspace applications include yielded wire grid antennas and yielded foilantennas,, which show little or no advantage over the prior artdescribed in detail herein.

SUMMARY OF THE INVENTION The instant invention utilizes a plurality ofspring loaded arms for deploying and supporting antenna surfaces. Thearms are folded against each other about a center post and are deployedby releasing a band or similar restraining device. The antenna surfacesare supported at the corners of a regularly shaped antenna or along thecircumference of a circular shaped antenna and at the central supporttube.

In the drawings:

DESCRIPTION OF THE DRAWINGS FIGURE 1 is a perspective view of theinvention;

FIGURE 2 is a top view, partly in phantom, of a preferred embodiment ofthe invention;

FIGURE 3 is a side elevational view, partly in phantom, of theinvention;

FIGURE 4 is an elevational drawing of the antennal tensioning mean shownalong the lines '44 in FIG- URE 3; and

FIGURE 5 is a side elevational view of the spring loaded joints used inthe antenna arms.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGURE 1, thereis shown generally a flat cavity-backed antenna 10. The antenna consistsof first and second flat surfaces 12 and 14 respectively. The surfacesare formed of flexible material, preferably a fabric or film or acombination of these materials. A preferred material which showssuperior results at an antenna is a film laminate of Kapton, aluminumand Komex fabric. The aluminum is etched or vapor-deposited to form theantenna spiral. This invention is, however, in no way meant to belimited to any particular fabric. The thickness of the spiral surfacemust be at least one electrical skin depth at the lowest frequency ofoperation.

Arms 16, 18, 20 and 22 extend outwardly from a center post 24. Thefabric material of surfaces 12 and 14 is securely mounted to the centerpost 24 and to the parallel extension of the arms at 26, 28, 30 and 32and held by resilient means 34 (FIGURE 3) which insures the propertension on the fabric at all times when in the extended position. Apreadjustable tension means is provided at 38 and will be describedhereinafter.

The surface 14 is a conducting surface and serves as a signal reflectorwhile surface 12 contains the conducting spirals of the antenna. Thespiral antenna surface 12 is attached near the end or top of each of thevertical members 26-32 while the reflector surface 14 is attached to 3the vertical members at a point below the spiral surface, parallel toit, and at the desired distance from it. The connection of surfaces 12and 14 to the center post 24 is similarly adjustable in the verticaldirection.

The center post 24 would be mounted at an appropriate location on thespacecraft or satellite. The lead-in Wires 40 from the antenna surfacesare located within the center post 24 and are suitably disposed forconnection to mating wires located on its base (not shown).

A top view of the antenna is shown in FIGURE 2. Spiral surface 12 iscompletely parallel and symmetrical to reflecting surface 14. Likewiseeach antenna surface is equally disposed around the center post 24 andheld tight by tension means such as an elastic cord 34.

In FIGURE 3 is shown a side elevation view of the invention with twophantom views indicating the position of the components in the closed orstored position, and the relative position of the various componentsduring its opening operation.

In the closed position shown generally at 40 the arms and fabric arefolded in such a manner that they are substantially parallel to andtouching the center post. The joints in the arms are Spring loaded byspring 52 shown in FIGURE and are held in position by strap 42. Inoperation, the strap 42 is released by a signal from earth or a timer orother conventional means. Upon release, the arms and fabric move in themanner indicated generally at 44. The joint at the center post 46 isspring biased and drives the inner portion (22A) of the arm downward'andis locked in position by means of a spring loaded pin in 5-4 shown onjoint 48 in FIGURE 5. At the same time the spring loaded joint 48 movesthe outer portion of the arm (22B) upwardly where it is locked inposition. Slightly before the movement of members 22A and 22B, thevertical member 30 is driven into position and locked by the springbiased joint 50. This occurs because of the manner in Which the arms arefolded in the closed position, member 30 is in contact with strap 42 andis the first member to sense the release of the strap. This sequence ofmotion insures that the fabric will not become tangled while unfoldingor due to a sudden strain caused by all joints locking at exactly thesame. moment.

The means for applying tension and insuring the parallelism of thesurfaces is shown in FIGURE 4. A collar 56 surrounds the member 30.Located in the collar is a set screw 58 which bears against the member30 for securing the collar. The resilient means 34 is attached to andwound around a shaft 60. This shaft is locked in position by means of aratchet (not shown) or alternatively by friction between the shaft andits mating hole. The shaft may therefore be turned and winds or unwindsthe resilient means changing the tension on the antenna surface. Thetensioning shaft is moved by hand or with and appropriate tool for thepurpose.

Although the invention has been described with reference to a particularembodiment, it will be understood to those skilled in the art that theinvention is capable of a variety of alternative embodiments within thespirit and scope of the appended claims.

We claim:

1. An expandable antenna comprising: a cylindrically shaped center postadaptable to be mounted on a space vehicle; collapsible arms mounted onthe center post, said arms, when expanded, consisting of a plurality ofhinged sections and extending transversely to the center post andfurther having a section hinged distally from the center post andparallel to it; flexible signal receiving means attached to the centerpost and to the said distally hinged section of the arm; flexiblereflector means attached to the center post and to the said distallyhinged section of the arm and parallel to the signal receiving means;and means for conducting a received signal from the antenna to a spacevehicle.

2. An antenna according to claim 1 wherein the hinged sections of thearms are spring biased.

3. An antenna according to claim 2 wherein the hinged sections of thearms are locked in the expanded position.

4. An antenna according to claim 1 wherein the flexible signal receivingmeans comprises a laminate of aluminum and a fabric.

5. An antenna according to claim 1 wherein the signal receiving meansand reflector means are attached to the distally hinged section of eacharm by an adjustable tension means.

6. An antenna according to claim 1 including a removable restrainingmeans for securing the arms and antenna and reflector surfaces in acollapsed condition.

References Cited UNITED STATES PATENTS 2,674,693 4/1954 Millett et a1343-915 X 2,763,002 9/1956 Fitzgerald et a1. 343880 ELI LIEBERMAN,Primary Examiner MARVIN NUSSBAUM, Assistant Examiner US. Cl. X.R.34388l, 897

